The load capacity of a foil thrust bearing depends on the compliance of the bearing with pressure exerted by a fluid film developed between the bearing and the runner. The pressure profile for a thrust bearing varies, and in order to accommodate the optimal pressure profile and attendant fluid film thickness associated with maximum load capacity, the thrust bearing should be designed to provide stiffness which varies in a manner similar to the pressure profile.
Current foil thrust bearings have limited load capacity, and this limitation results from spring designs which indicate only a limited appreciation for variance in pressure profile and its effect on load capacity.
A typical spring design is illustrated in FIGS. 2-6 of U.S. Pat. No. 4,668,106 Gu. While such spring designs provide varying stiffness in radial directions, they provide limited load capacity because of excess pad deflection over the spring support points. The excessive pad deflection leads to a divergent fluid film at the trailing edge of the pad and prevents the bearing from developing an optimal pressure profile. Thus, the advantages associated with providing varying stiffness in both radial and circumferential directions has gone unrecognized.
An objective of this invention is to provide foil thrust bearings with stiffness variation in both radial and circumferential directions.
A further objective of the invention is to provide such stiffness variation in a manner which approximates pressure profiles in both radial and circumferential directions.
Concomitant objectives of the invention are to extend the range of potential applications for foil bearings, and to enable the use of smaller foil bearings in a given application.